Cardiac output, circulating blood volume, and resting oxygen consumption are all increased in the obese; however, total blood flow is sub-normal in relation to body weight. Obesity augments the size of individual fat cells without increasing blood flow. Specifically, fat tissue is hypoperfused and poorly oxygenated. Intraoperative tissue oxygenation is abnormally low in obese patients and postoperative tissue oxygenation is especially low — although it can be improved by oxygen administration. It thus seems likely that inadequate tissue oxygenation contributes to the observed extraordinary high wound infection risk in obese patients.